Generating default DKIM keys: Cannot determine host's domain name, so skipping default key generation

I'm following this guide https://www.linuxtechi.com/configure-domainkeys-with-postfix-on-centos-7/ When I get to this section, it gives an error # opendkim-default-keygen Generating default DKIM keys: Cannot determine host's domain name, so skipping default key generation. I do have my hostname set # hostname domain.org # cat /etc/hostname domain.org # cat /etc/hosts # Your system has configured 'manage_etc_hosts' as True. # As a result, if you wish for changes to this file to persist # then you will need to either # a.) make changes to the master file in /etc/cloud/templates/hosts.redhat.tmpl # b.) change or remove the value of 'manage_etc_hosts' in # /etc/cloud/cloud.cfg or cloud-config from user-data # # The following lines are desirable for IPv4 capable hosts 127.0.0.1 domain domain.org 127.0.0.1 localhost.localdomain localhost 127.0.0.1 localhost4.localdomain4 localhost4 # The following lines are desirable for IPv6 capable hosts ::1 domain domain.org ::1 localhost.localdomain localhost ::1 localhost6.localdomain6 localhost6 # cat /etc/sysconfig/network NETWORKING=yes HOSTNAME=domain.org NOZEROCONF=yes (I replaced all instances of the domain name with domain.) Other pages on the web only say to set the hostname, which is set. # cat /etc/centos-release CentOS Linux release 7.5.1804 (Core)